Add fewer_rows_then schema test

* Macro and test case

* Update fewer_rows_than.sql

* Update for dev/0.7.0 changes

* Update changelog (skip ci)

Co-authored-by: Dan M <47741043+dmarts@users.noreply.github.com>

Author: Claire Carroll

CHANGELOG.md

@@ -6,6 +6,7 @@
 * Make `expression_is_true` work as a column test (code originally in [#226](https://github.com/fishtown-analytics/dbt-utils/pull/226/) from [@elliottohara](https://github.com/elliottohara), merged via [#313])
 * Allow individual columns in star macro to be aliased (code originally in [#230](https://github.com/fishtown-analytics/dbt-utils/pull/230/) from [@elliottohara](https://github.com/elliottohara), merged via [#245])
 * Add new schema test, `not_accepted_values` ([#284](https://github.com/fishtown-analytics/dbt-utils/pull/284) [@JavierMonton](https://github.com/JavierMonton))
+* Add new schema test, `fewer_rows_than` (code originally in [#221](https://github.com/fishtown-analytics/dbt-utils/pull/230/) from [@dmarts](https://github.com/dmarts), merged via [#343])
 
 
 ## Fixes

README.md

@@ -95,7 +95,7 @@ Usage:
 ---
 ### Date/Time
 #### date_spine ([source](macros/datetime/date_spine.sql))
-This macro returns the sql required to build a date spine. The spine will include the `start_date` (if it is aligned to the `datepart`), but it will not include the `end_date`. 
+This macro returns the sql required to build a date spine. The spine will include the `start_date` (if it is aligned to the `datepart`), but it will not include the `end_date`.
 
 Usage:
 ```
@@ -132,6 +132,20 @@ models:
 
 ```
 
+#### fewer_rows_than ([source](macros/schema_tests/fewer_rows_than.sql))
+This schema test asserts that this model has fewer rows than the referenced model.
+
+Usage:
+```yaml
+version: 2
+
+models:
+  - name: model_name
+    tests:
+      - dbt_utils.fewer_rows_than:
+          compare_model: ref('other_table_name')
+```
+
 #### equality ([source](macros/schema_tests/equality.sql))
 This schema test asserts the equality of two relations. Optionally specify a subset of columns to compare.
 
@@ -181,13 +195,13 @@ models:
 
 ```
 
-This macro can also be used at the column level. When this is done, the `expression` is evaluated against the column.  
+This macro can also be used at the column level. When this is done, the `expression` is evaluated against the column.
 
 ```yaml
 version: 2
-models: 
+models:
     - name: model_name
-      columns: 
+      columns:
         - name: col_a
           tests:
             - dbt_utils.expression_is_true:
@@ -197,7 +211,7 @@ models:
             - dbt_utils.expression_is_true:
                 expression: '= 1'
                 condition: col_a = 1
-      
+
 ```
 
 
@@ -361,7 +375,7 @@ models:
           upper_bound_column: ended_at
           partition_by: customer_id
           gaps: required
-  
+
   # test that each customer can have subscriptions that start and end on the same date
   - name: subscriptions
     tests:
@@ -497,9 +511,9 @@ constraint needs to be verified.
 
 
 #### accepted_range ([source](macros/schema_tests/accepted_range.sql))
-This test checks that a column's values fall inside an expected range. Any combination of `min_value` and `max_value` is allowed, and the range can be inclusive or exclusive. Provide a `where` argument to filter to specific records only. 
+This test checks that a column's values fall inside an expected range. Any combination of `min_value` and `max_value` is allowed, and the range can be inclusive or exclusive. Provide a `where` argument to filter to specific records only.
 
-In addition to comparisons to a scalar value, you can also compare to another column's values. Any data type that supports the `>` or `<` operators can be compared, so you could also run tests like checking that all order dates are in the past. 
+In addition to comparisons to a scalar value, you can also compare to another column's values. Any data type that supports the `>` or `<` operators can be compared, so you could also run tests like checking that all order dates are in the past.
 
 Usage:
 ```yaml
@@ -513,19 +527,19 @@ models:
           - dbt_utils.accepted_range:
               min_value: 0
               inclusive: false
-      
+
       - name: account_created_at
         tests:
           - dbt_utils.accepted_range:
               max_value: "getdate()"
               #inclusive is true by default
-      
+
       - name: num_returned_orders
         tests:
           - dbt_utils.accepted_range:
               min_value: 0
               max_value: "num_orders"
-      
+
       - name: num_web_sessions
         tests:
           - dbt_utils.accepted_range:

integration_tests/data/schema_tests/data_test_fewer_rows_than_table_1.csv

@@ -0,0 +1,4 @@
+field
+1
+2
+3

integration_tests/data/schema_tests/data_test_fewer_rows_than_table_2.csv

@@ -0,0 +1,5 @@
+field
+1
+2
+3
+4

integration_tests/models/schema_tests/test_fewer_rows_than.sql

@@ -0,0 +1,9 @@
+with data as (
+
+    select * from {{ ref('data_test_fewer_rows_than_table_1') }}
+
+)
+
+select
+    field
+from data

macros/schema_tests/fewer_rows_than.sql

@@ -0,0 +1,43 @@
+{% macro test_fewer_rows_than(model) %}
+  {{ return(adapter.dispatch('test_fewer_rows_than', packages = dbt_utils._get_utils_namespaces())(model, combination_of_columns, quote_columns, where)) }}
+{% endmacro %}
+
+{% macro default__test_fewer_rows_than(model) %}
+
+{% set compare_model = kwargs.get('compare_model', kwargs.get('arg')) %}
+
+with a as (
+
+    select count(*) as count_ourmodel from {{ model }}
+
+),
+b as (
+
+    select count(*) as count_comparisonmodel from {{ compare_model }}
+
+),
+counts as (
+
+    select
+        (select count_ourmodel from a) as count_model_with_fewer_rows,
+        (select count_comparisonmodel from b) as count_model_with_more_rows
+
+),
+final as (
+
+    select
+        case
+            -- fail the test if we have more rows than the reference model and return the row count delta
+            when count_model_with_fewer_rows > count_model_with_more_rows then (count_model_with_fewer_rows - count_model_with_more_rows)
+            -- fail the test if they are the same number
+            when count_model = count_comparison then 1
+            -- pass the test if the delta is positive (i.e. return the number 0)
+            else 0
+    end as row_count_delta
+    from counts
+
+)
+
+select row_count_delta from final
+
+{% endmacro %}